Production of shrunk leather



United States Patent 3,010,779 PRODUCTION OF SHRUNK LEATHER Ernst Komarek, Leverkusen, and Gustav Mauthe, Op-

laden, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany 7 No Drawing. Filed Mar. 13, 1959, Ser. No. 799,117

Claims priority, application Germany Mar. 22, 1958 1 Claim. (Cl. 8-94.18)

The present invention relates to and has as its objects the preparation of leather with artificial shrunk grains or so called shrunk leather. Generally the compounds which may be used in the course of the preparation of said leather are condensation products obtained from dihydroxy-diphenyl-sulfon resins containing still free methylol groups and naphthalene sulfonic acids.

Shrunk leather recently became a new standard leather and especially is an important material for the manufacture of shoes and fashion leather materials. The effect of the shrunk grain of these leathers is variable in wide limits. The grain may be flat and large but on the other hand its also may be very fine and deep. The size and the effect of shrunk grain mostly depends on the thickness and on the water contents of the pelts. The thinner the pelts and the more they are sammed the finer the grain will be. On the other hand also the concentration of the shrunk tanning is of importance for the grain. The higher the concentration of the shrunk tanning is the finer and the higher is also the shrunk grain. A pelt which contains more Water or a shrunk tanning liquor which is more diluted will have a fiat and less pronounced grain.

Shrink tannage previously has been performed with vegetable as well as with synthetic resins. In practice, however, as a vegetable tannin only sumac tannin has been used. The disadvantage of this tannin is its deep color and its behaviour against alkali liquors and iron salts. The practical use of sumac therefore also is limited to some respect.

Synthetic sulfo-group containing tannins which have been used as yet for the preparation of shrunk leather are especially the commercially available tannins for the preparation of white leather. Those are especially the sodium or ammonium salts of the condensation products of 4.4-dihydroXy-diphenyl sulfon and naphthalene sulfonic acid and formaldehyde which have been slightly acidified by organic acids such as acetic acid, formic acid and the like.

The results which have been obtained with the aforementioned tanning agents, however, were not satisfying in every respect. It is difiicult e.g. to control the efiect of shrinking and it has been especially diflicult to obtain a very fine shrunk grain with the above mentioned tanning agents. Especially disadvantageous is the unequality of the grain if leather is prepared according to the above mentioned processes. This unequality means that reacting the complete area of hides or skins the degree of shrinkage varies considerably according to the origin of the material. This unevenness mainly is caused by structural differences of the skin. An unequal shrunk leather with different grain is not useful for the preparation of quality shoes and losses of leather therefore are considerably high.

In accordance with the present invention it has now been found that high quality shrunk leather may be obtained if the hide is pretreated with condensation products obtained from dihydroxy-diphenyl sulfon resins containing free methylol groups and naphthalene sulfonic acids and wherein those condensation products are present completely or to a considerable degree in the form of their free sulfonic acids. Considerable free sulfonic ice.

acid in the meaning of the abovesaid in a pH value of a diluted solution of the above said sulfonic acids of at least 2.

Free methylol group-containing dihydroXy-diphenyl sulfon resins in the meaning of the presentinvention are condensation products obtained from dihydroxy-diphenyl sulfons or corresponding polysulfons with form-aldehyde in an alkaline reacting 'medium, at higher temperatures e.g. in the boil. The alkaline reacting substance which is necessary as a catalyst may be removed by careful neutralization and separation of the resin, but it may also be left in the reaction medium to neutralize free sulfuric acid contained in the second reaction product, namely the naphthalene sulfonic acid. The preparation of condensation products of this type has been described e.g. in United States Patents Nos. 2,716,098 and 1,972,- 754.

The temperature and the reaction time of the aforementioned resins with naphthalene sulfonic acids may vary in wide limits. A naphthalene sulfonic acid in the meaning of this invention is the mixture of different acids obtained in the known sulfonation of naphthalene with sulfuric acids at higher temperatures e.g. as described in United States Patents Nos. 1,972,754 and 2,716,098.

The optional condensation conditions may be determined according to the sulfone resin i.e. to the degree of the condensation of the polysulfon resin. Usually temperatures between and C. and a condensation time between 1 and about 2 hours is optional for obtaining the condensation products used for the inventive preparation of shrunk leather.

It has been found that the above said synthetic sulfogroup containing resins are considerably better shrink tannins compared with their salts adjusted by addition of strong acids to a pH value of 2. A shrunk efiect may be obtained also with the known salts of the above said free sulfonic acids if these salts are mixed with strong acids. But the effect of equality is far removed from the shrunk efiect obtained according to this invention. According to the present invention there is obtained a very equal grain which may still be varied in wide limits without harming the quality and equality of the grain within the whole area of the skin treated. It is indeed remarkable that small amounts of the above described products already lead to a fine shrunk grain of high equality.

The following examples may illustrate this invention, without, however, limiting itin any way:

EXAMPLE 1 Preparation of cow shrunk leather Cow hides are treated in the lime house in the usual manner for the preparation of cow leather. According to the desired grain they are split to 3-4 mm. After deliming, wetting and samming they are drummed in a rotating drum (about 15 rotations per minute). This drumming operation is carried out with 12% (referred to the weight of the split leather) of the condensation product described below and 12% of water for 2 hours. At this stage the shrunken hides are tanned with a chromium tannin containing 2% of chromium oxide referring to the split weight of the skin. The chromium tannin has a basicity of or 33%.

Tanning is continued in the usual manner for the preparation of cow leather and final treatment such as neutralization, dyeing, liquoring and the like leads to a very equal shrunk leather with an excellent plumpness. The preparation of the above said shrunk tannin has been carried out as follows: 500 parts by weight of 4.4- dihydroxy-diphenylsulfon are suspended in 300 parts by weight of water and 70 parts by weight of a sodium hydroxide solution (45%). To this mixture there are Preparation of calf shrunk leather Calf hides are treated in the lime house as usual for the preparation of calf leather. The well sammed hides are drummed in a quickly rotating drum with of saw dust referred to the crude weight of the skin for'30 minutes and therefrom with 8% of the condensation production described in the foregoing example and 8% of water. The last drumming operation is continued for 2 further hours. The calf skin treated in this way now is chromium tanned, neutralized, dyed and fat-liquored in the usual way. The, leather thus obtained has a fine and equal shrunk grain and-is soft and smooth.

EXAMPLEJ 7 Preparation of goat shrunk leather Goat skins treated in the lime house in the usual way after samming are treated in a quickly rotating drum with 5% of saw dust for 20 minutes. Therefrom 12% of a condensation product as described in Example 1 and 12% of water are added and the drumming operation is continued for 2 further hours. After this the usual chromium tannin follows. The goat shrunk leather thus obtained is very even.

I claim: V

I A process for the production of shrunk leather which comprises treating a member selectedtfro'm the group consisting of hides and skins with an aqueous solution of a condensation product of a member selected from the group consisting of dihydroxy-diphenyl sulfon and polyhydroxy polyphenyl sulfon resins containing free methylol groups and naphthalene sulfonic acid, said treatment being conducted at a pH value below 2 whereby the hide is transformed into a shrunken form, and then tanning the shrunk hide in the usual Way with a chromium tannin to complete the preparation of shrunk leather.

References Cited in the file of this patent UNITED STATES PATENTS 1,972,754 Biedermann Sept. 4, 1934 2,592,587 Nagy Apr. 15, 1952 2,716,098 Biedennann Aug. 23, 1955 2,781,241 Ushakofi Feb. 12, 1957 OTHER REFERENCES McLaughlin et al.: The Chemistry of Leather Manufacture, pp. -127. 

